DE 10 2009 008 255 A1 discloses a method for stabilizing an on-board energy system of a motor vehicle or a commercial vehicle. During operation of the method, a first voltage is applied to a first on-board power system branch, with a first energy store, a generator for supplying the first energy store and at least one first load being connected to the first on-board power system branch. A second voltage which is higher than the first voltage is applied to a second on-board power system branch, with a second energy store, a charging unit for supplying the second energy store, which is also coupled to the first on-board power system branch, and at least one second load being connected to the second on-board power system branch, the first and second energy stores being connected in series with one another in order to generate the second voltage. In order to control the output voltage and the output current of the charging unit, at least the first and second voltages are measured by a respective measuring element, from which a charging current for the second energy store is determined and generated. Finally, the measured first and/or second voltage(s) is/are conditioned using a non-linear element in such a manner that the charging unit charges the second energy store with increased energy withdrawal from the first on-board power system branch in the event of voltage rises of the first voltage and/or charges the second energy store with reduced energy withdrawal from the first on-board power system branch in the event of voltage dips of the first voltage.